slapd-relay - relay backend to slapd
/etc/ldap/slapd.conf
The primary purpose of this
slapd(8) backend is to map a naming context
defined in a database running in the same
slapd(8) instance into a
virtual naming context, with attributeType and objectClass manipulation, if
required. It requires the
slapo-rwm(5) overlay.
This backend and the above mentioned overlay are experimental.
The following
slapd.conf directives apply to the relay backend database.
That is, they must follow a "database relay" line and come before
any subsequent "backend" or "database" lines. Other
database options are described in the
slapd.conf(5) manual page; only
the
suffix directive is allowed by the
relay backend.
- relay <real naming context>
- The naming context of the database that is presented under
a virtual naming context. The presence of this directive implies that one
specific database, i.e. the one serving the real naming context,
will be presented under a virtual naming context.
The
relay database does not automatically rewrite the naming context of
requests and responses. For this purpose, the
slapo-rwm(5) overlay must
be explicitly instantiated, and configured as appropriate. Usually, the
rwm-suffixmassage directive suffices if only naming context rewriting
is required.
One important issue is that access rules are based on the identity that issued
the operation. After massaging from the virtual to the real naming context,
the frontend sees the operation as performed by the identity in the real
naming context. Moreover, since
back-relay bypasses the real database
frontend operations by short-circuiting operations through the internal
backend API, the original database access rules do not apply but in selected
cases, i.e. when the backend itself applies access control. As a consequence,
the instances of the relay database must provide own access rules that are
consistent with those of the original database, possibly adding further
specific restrictions. So, access rules in the
relay database must
refer to identities in the real naming context. Examples are reported in the
EXAMPLES section.
If no
relay directive is given, the
relay database does not refer
to any specific database, but the most appropriate one is looked-up after
rewriting the request DN for the operation that is being handled.
This allows one to write carefully crafted rewrite rules that cause some of the
requests to be directed to one database, and some to another; e.g.,
authentication can be mapped to one database, and searches to another, or
different target databases can be selected based on the DN of the request, and
so.
Another possibility is to map the same operation to different databases based on
details of the virtual naming context, e.g. groups on one database and persons
on another.
To implement a plain virtual naming context mapping that refers to a single
database, use
database relay
suffix "dc=virtual,dc=naming,dc=context"
relay "dc=real,dc=naming,dc=context"
overlay rwm
rwm-suffixmassage "dc=real,dc=naming,dc=context"
To implement a plain virtual naming context mapping that looks up the real
naming context for each operation, use
database relay
suffix "dc=virtual,dc=naming,dc=context"
overlay rwm
rwm-suffixmassage "dc=real,dc=naming,dc=context"
This is useful, for instance, to relay different databases that share the
terminal portion of the naming context (the one that is rewritten).
To implement the old-fashioned suffixalias, e.g. mapping the virtual to the real
naming context, but not the results back from the real to the virtual naming
context, use
database relay
suffix "dc=virtual,dc=naming,dc=context"
relay "dc=real,dc=naming,dc=context"
overlay rwm
rwm-rewriteEngine on
rwm-rewriteContext default
rwm-rewriteRule "dc=virtual,dc=naming,dc=context"
"dc=real,dc=naming,dc=context" ":@"
rwm-rewriteContext searchFilter
rwm-rewriteContext searchEntryDN
rwm-rewriteContext searchAttrDN
rwm-rewriteContext matchedDN
Note that the
slapo-rwm(5) overlay is instantiated, but the rewrite rules
are written explicitly, rather than automatically as with the
rwm-suffixmassage statement, to map all the virtual to real naming
context data flow, but none of the real to virtual.
Access rules:
database mdb
suffix "dc=example,dc=com"
# skip...
access to dn.subtree="dc=example,dc=com"
by dn.exact="cn=Supervisor,dc=example,dc=com" write
by * read
database relay
suffix "o=Example,c=US"
relay "dc=example,dc=com"
overlay rwm
rwm-suffixmassage "dc=example,dc=com"
# skip ...
access to dn.subtree="o=Example,c=US"
by dn.exact="cn=Supervisor,dc=example,dc=com" write
by dn.exact="cn=Relay Supervisor,dc=example,dc=com" write
by * read
Note that, in both databases, the identities (the
<who> clause) are
in the
real naming context, i.e.
`dc=example,dc=com', while the
targets (the
<what> clause) are in the
real and in the
virtual naming context, respectively.
The
relay backend does not honor any of the access control semantics
described in
slapd.access(5); all access control is delegated to the
relayed database(s). Only
read (=r) access to the
entry
pseudo-attribute and to the other attribute values of the entries returned by
the
search operation is honored, which is performed by the frontend.
- /etc/ldap/slapd.conf
- default slapd configuration file
slapd.conf(5),
slapd-config(5),
slapo-rwm(5),
slapd(8).